Just curious, is there anything that can prevent developers to charge 30% more when in-app purchase is used for sign-up, with a nice little text around the 'Buy

Just curious, is there anything that can prevent developers to charge 30% more when in-app purchase is used for sign-up, with a nice little text around the 'Buy' button: You would get 30% discount if you use our website for purchase. Here the price includes Apple payment infrastructure cost. I'm sure there would not be anything in Apple's guideline documents about adding above kind of 'informative' content.